The impacts of dust on health, agriculture, ecosystems, recreation, and so on, will extend into the future with influence from climate change and land and water management policy. However, due to the complex dynamics underlying dust generation and transport, our understanding of how dust storms will change in the future remains limited. Here, we discuss how environmental drivers and natural resource management are likely to shape dust in California over the coming years to decades.
Climate Change
Climate change is expected to increase dust storms in the southwestern parts of the United States, including California. This is because dust emissions are affected by environmental drivers, such as precipitation, soil moisture, surface temperature, and surface winds, which are projected to change as the planet continues to warm. For example, precipitation extremes are projected to intensify, along with more frequent and extreme dry-to-wet events, increasing the risk of both flood and drought in California. Future drought conditions could result in changes in soil characteristics, such as reducing soil moisture, potentially leading to changes in dust emissions in California’s arid and semi-arid regions. For example, drought-induced changes in soil characteristics was attributed to recent increases in dust concentration around Owens Lake between 2013 and 2015 . Flooding can enhance the transport of dust-sized sediment downstream and over dry lakes, which may increase the susceptibility of dust emissions after they become dry. Elevated surface temperatures due to greenhouse gases can greatly amplify seasonal dryness and moisture loss in the atmosphere and soil, resulting in increased severity of drought conditions, degradation of protective desert soil crust, and increases in associated dust activities. Changes in the near-surface wind speeds that drive dust emissions are projected to be small and variable, depending on the season and location.
Shifts in global-to-regional circulation patterns caused by the changing climate are also likely to influence dust emission in the future. For example, the increasing frequency of strong El Niño/Southern Oscillation events due to the warming climate is likely to result in more frequent periods of below average rainfall across the Western US that are associated with La Niña-like conditions, and thus an increase in dust in the year following these dry periods. In southeastern California projections of a weakening North American Monsoon imply a potential reduction in summertime dust storms there, although these results are in seemingly in contradiction to historical increases in the intensity of monsoonal precipitation, suggesting a high level of uncertainty in the connections between climate change, regional circulation patterns, and dust.
Landscape Disturbance
In addition to these environmental factors that may dominate future dust emissions from natural desert sources like dry lakebeds and dry washes, human-induced factors may also influence dust emissions from so-called anthropogenic sources, such as construction, off-road vehicle use, and agriculture. The California Air Resources Board’s California Emissions Projection Analysis Model (CEPAM) (California Air Resources Board, 2019) projects that dust from these anthropogenic sources will increase by approximately 45% in 2050, relative to the 2017 baseline. This increase in dust emission is projected to mostly come from construction, demolition, and resuspensions from paved roads. In contrast, CEPAM suggests that dust emissions from unpaved roads, fugitive windblown dust from croplands and pasturelands, and farming operations, such as tilling and harvest, will remain approximately the same or decrease by less than 7% in the coming decades. Because these future dust emission projections depend on the 2017 base year emission inventory and emission factors model, they are subject to substantial uncertainties. While CEPAM may project minimal changes in anthropogenic dust from agricultural croplands, historically, poor agricultural management and practices have been linked to major wind-blown dust or dust storms. For Example, the dust event of November 1991 that led to a collision of 164 vehicles and 17 fatalities on Interstate 5 in the San Joaquin Valley was thought to be wind-blown dust from agricultural sources likely aided by inadequate land management. Therefore, changes in agricultural land management and practices could alter future changes in anthropogenic dust emissions, particularly in California’s Central Valley where a majority of the state’s agricultural sources are located. For example, changes in tillage, fallowing, and grazing could expose vast swathes of farm cropland to wind erosion and contribute to desertification and dust production, echoing some of the conditions that lead to the Dust Bowl. Because the contribution to dust emission from anthropogenic sources is likely substantial, understanding the large uncertainties in the projection of anthropogenic dust emission is key to estimate the future of dust in California.
Other Changes in Natural Resources Management
In addition to factors that can affect dust emissions, changes in government policies can also influence agricultural land-use management practices with direct consequences for wind erosion. A report from the Public Policy Institute of California suggested that to achieve the goals of the state’s 2014 Sustainable Groundwater Management Act, instituted to bring groundwater basins into balance in the next two decades, between 0.5-1 million acres of irrigated land will need to be fallowed (Hanak et al., 2019). Such fallowed cropland could become new dust sources that may increase dust emission and surface concentrations particularly in the Central Valley. Additionally, Southern California dustiness is susceptible to climate-change driven policies in water transfer and storage. For example, global warming drives the long-term decline in Colorado River levels by aridifying the basin’s snowpack regions. Climate models project that this drying will intensify toward the end of this century. This will exacerbate pressure on agricultural users, who consume more than two-thirds of California’s Colorado River allocation, to increase fallowing and to reduce irrigation. Both of these actions tend to increase dust emission. Irrigation runoff has been the only source of water to the Salton Sea since the Quantification Settlement Agreement of 2003 ended the direct transfer of Colorado River water to the Sea in 2017. The Sea’s level has since transitioned from a period of gradual decline to a new era of rapid decline that is estimated to expose about 40% of the year 2000 lakebed to wind erosion by 2030, reaching about 100,000 acres of exposed lakebed by 2050 when levels may stabilize. Dust deflated from the exposed playa may increase PM10 in the surrounding region by about 10% by 2030, and by much more in localized source areas.
Broadly over California, a projected increase in dust emissions and activities is expected to have significant impacts on the Sierra Nevada snowpack, hydrology, air quality, and public health. As previously discussed, dust deposition onto the Sierra Nevada snowpack can accelerate snowmelt by reducing surface albedo , particularly in spring and summer, when dust activities are high across major sources that transport dust to the Sierra Nevada. Such a decrease in Sierra Nevada snowpack could, in turn, exacerbate California’s water scarcity, negatively impacting crucial water reservoirs that feed into the state’s water supply system, particularly during future drought years. In addition, an increase in future dust storms can significantly degrade air quality by elevating fine particulate matter concentrations that could trigger more respiratory illnesses and increase hospital admissions for asthma and chronic obstructive pulmonary disease, especially for underserved communities in California’s Central Valley (see the Impacts of Dust Storms Section of this report for more detail). Understanding future changes in sources, transport pathways, and composition of dust aerosols will be crucial for mitigating impacts on Sierra Nevada snowpack, air quality and regional climate across California.
Summary
The future of dust in California is expected to worsen under climate change. This is because common environmental drivers that influence dust emission, such as precipitation, soil moisture, surface temperature, and surface winds, are all projected to change under climate change in a way that is likely to drive an increase in dust emissions. In addition, changes in land use management, influenced by climate change, current or future government policies may also have indirect impacts on future dust emission in California. In particular, water management initiatives like the 2014 California’s Sustainable Groundwater Management Act, could necessitate the fallowing of million acres of irrigated land, potentially creating new dust sources. Overall, understanding the complex dynamics behind dust generation and likely occurrence of new emission sources is crucial for developing effective mitigation strategies.
